It has long been desired to find an inexpensive means of making alkyl methacrylate and alkyl acrylates, basic monomers for the formation of acrylic resins, as well as acrylic and methacrylic acids. Conventionally, methyl methacrylate is prepared by reacting acetone and hydrogen cyanide to form cyanohydrin; dehydrating the cyanohydrin in the presence of sulphuric acid to form methacrylamide sulfate; and finally reacting the sulfate with methanol and sulphuric acid to form the desired methyl methacrylate. Because of the high cost of the raw materials and the need to dispose of by-product ammonium sulfate, this process is deficient.
Other proposed processes for making methyl methacrylate and methacrylic acid involve isobutylene oxidation, ammoxidation, epoxide formation and t-butanol oxidation. These processes also suffer from high capital costs and, in some cases, raw material costs.
In assignee's co-pending application Ser. No. 28,460 filed this even date entitled "BF.sub.3 Complex Catalyst for Preparing Acids and Esters," a process is described for making carboxylic acid esters, e.g., alkyl methacrylates and alkyl acrylates, by the carbonylation of ethylene or propylene with carbon monoxide in the presence of a catalyst complex composed of one mole of methanol and the olefin propylene, the product is methyl isobutyrate. This latter compound may be dehydrogenated to prepare methyl methacrylate. This process is advantageous because the end products are formed from raw materials, no by-products are formed, and the capital costs are economically attractive.
The process described in the aforesaid co-pending application, while extremely attractive for the foregoing reasons, suffers from the drawback that catalyst complex could not be easily recovered for reuse. As a matter of fact, in discussing this specific catalyst for use with cyclic olefins, Moller in Brennstoff-Chemie 45, 129 (1964), said that the catalyst BF.sub.3.CH.sub.3 OH would be of little interest because it cannot be recovered in usable form. This is because there is no known way to separate the reacting ester product from the complex without destroying the BF.sub.3, e.g., by hydrolyzing it with water to form fluoroboric acids.